It is generally agreed that the single-acting two piston Stirling engine is one of the most desirable forms of Stirling for small power applications, having demonstrated both simplicity and good performance. Such engines may be designed in a variety of forms; for example, cylinders may be in a V, in-line, or horizontally opposed arrangement.
One of the most desirable arrangements is the inverted yoke drive described by Ross in U.S. Pat. No. 4,532,819. In this design the upper apex of a triangular yoke is attached to a single-throw crankshaft located beneath twin parallel cylinders. The lower portion of the yoke is constrained by a rocking lever. The lower apexes of the yoke are attached by connecting rods to the respective pistons. Practically all of the side loads encountered in this mechanism are absorbed by the rocking lever bearings. The pistons themselves see very low side loads, and therefore they may be run without liquid lubrication, yet still give long life with low friction losses. The ability to run well without liquid lubrication is an important advantage in a Stirling engine.
Inverted yoke drive Stirling engines have in fact demonstrated excellent mechanical efficiency, and their overall size and weight are considerably less than that of two-piston engines of other configurations, for a given presure level and power.
The aim of this invention is to disclose a new form of yoke-based crank drive mechanism for the two-piston Stirling which offers a considerable reduction of cost, complexity, and reciprocating weight in a given engine, and yet retains all the known advantages of the previous inverted yoke drive mechanism.
Other aims, features, and advantages will be apparent in the description below.